1. Field of the Invention
The present invention relates to a method of making a stabilizer bar for a vehicle and to the stabilizer bar made according to the method.
2. Background Art
A stabilizer bar is a vehicle suspension component that forms part of the front suspension. A stabilizing bar is a hollow rigid bar that interconnects front suspension elements with the frame of the vehicle to improve stability.
A stabilizer bar has eyelets on opposite ends for receiving fasteners for connecting the bar to the suspension for the right wheel and left wheel. Stabilizer bars are formed from hollow tubes in a hot forming process. After forming, they are quenched in an oil bath or aqueous bath and then are annealed. One problem with prior art stabilizer bar manufacturing techniques is that if the stabilizer bar end is not completely closed prior to quenching, the quenching oil or aqueous solution may be drawn into the tube due to a vacuum created when the hot tube is cooled and becomes trapped within the tube. This can result in what appears to be an oil leak if the quench fluid later drips from the stabilizer bar. This can lead to unnecessary warranty costs if a customer believes that they have an oil leak but service technicians are unable to identify the source of the oil since the stabilizer bar is intended to be a hollow tube that does not ordinarily contain oil or other fluid.
Another problem encountered in the manufacture of stabilizer bars is that if they have ends formed by squeezing a hollow tube to form a closed end it is difficult to maintain alignment of the top and bottom wall holes after forming and thermal treatment. If two holes are pierced through the two walls of a tube they may initially be aligned but as the tube is subsequently bent, quenched and annealed the two holes may become misaligned.
One solution to the above problems has been to fill the ends of the tube used to manufacture the stabilizer bar with a solid metal cylindrical piece, or filler slug, that extends into the tube from both ends approximately 1 to 2 inches. The ends of the tube are then spin welded to the filler slug to provide a tube having solid ends that can be formed and trimmed to form the fastener eyelets. A stabilizer bar having spin welded tube end fillers can be quenched without any risk of drawing the quench fluid into the hollow tubular portion of the stabilizer bar. The problem of misalignment of the two holes after forming is also solved by welding the cylindrical piece to the tube end is also avoided. However, this approach adds to the cost of materials required to make the stabilizer bar and also adds manufacturing operations that make it more expensive to produce a stabilizer bar.
There is a need for a method of making stabilizer bars having closed ends that do not draw quench fluid into the stabilizer bar during the manufacturing process that can result in difficult to identify oil leaks in a vehicle. More generally, there is a need for an improved manufacturing process for manufacturing parts from tubes having closed ends that do not distort the alignment of the holes in the ends when the tube is subsequently hot formed and quenched. Tubes fabricated in a hot forming process followed by a quenching operation may be used in applications other than the manufacture of stabilizer bars. Other such tube fabricating processes can benefit from a simple and inexpensive process for closing and sealing tube ends.
The above problems and needs are addressed by the invention as summarized below.
According to one aspect of the present invention, a method of making a stabilizer bar for a vehicle is provided that comprises initially providing a steel tubular member having an inner diameter and two open ends. A mixture of an adhesive and a fuseweld powder is applied to the inner diameter of both ends of the tubular member. The adhesive may be cured if applied in a wet state and the tubular member is heated to cause the fuseweld powder to melt. The two ends of the tubular member are formed by flattening to form two flat ends while the fuseweld powder is heated to at least a temperature wherein the fuseweld powder is in a plastic state. The method is completed by trimming each of the two ends to form an eyelet for a fastener.
According to other aspects of the invention, the fuseweld powder may be a powdered metal composition such as a mixture of powdered metal such as chromium, nickel, boron, silicon and molybdenum. Other additives may include small amounts of cobalt, carbon, iron, or tungsten that may be used to change the final product properties such as the required ductility. The step of applying the mixture adhesive and fuseweld powder may be performed by either brushing or spraying the mixture to apply to the inner diameter of the two ends of the tubular member. Alternatively, if the mixture is applied just prior to melting and forming other methods of applying the mixture may be used including inserting in a glass or silicone capsule containing the fuseweld powder that melts within the tube end and can function as a flux. The mixture may also be applied just prior to further processing by a metered injection of a dry powder, thick slurry or in a gel form. The mixture could also be applied by a thermal spray process and then subsequently remelted. The step of forming the two ends to form two flat ends may further comprise swaging each of the two ends together with the fuseweld powder sealing the two ends of the tubular member.
According to another aspect of the invention, the method may also include reheating the tubular member and bending the tubular member along its length while heated. After bending, the tubular member is quenched in a quenching fluid and then annealed. The tubular member may be quenched while the fuseweld powder seals the two ends of the tubular member to prevent the quenching fluid from being drawn into the tubular member.
According to another aspect of the invention, a stabilizer bar is provided for a vehicle that comprises a tubular member having two ends and an opening extending between the two ends. Each of the two ends is provided with a mixture of an adhesive and a fuseweld powder on their inner diameters. Each of the ends have flat portions that are bonded together by the fuseweld powder to form a seal. The stabilizer bar further includes openings for receiving a fastener provided on each of the ends of the stabilizer bar. Bonding the ends prevents the openings in the stabilizer bar ends from becoming misaligned after forming and heat treating. The fuseweld powder sealing the ends of the stabilizer bar may be a powdered metal composition including chromium, nickel, boron, silicon and molybdenum. Other additives may include small amounts of cobalt, carbon, iron, or tungsten. The fuseweld powder bonds the two ends of the tubular member and the boron or silicon may function as a flux agent that facilitates bonding to the tubular member.
The aspects of the invention summarized above and additional features of the invention are more specifically described with reference to the attached drawings and following detailed description thereof.